Municipal Wastewater Treatment Plant - Water Engineering - Old Exam Paper, Exams of Structures and Materials

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CORK INSTITUTE OF TECHNOLOGY

INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ

Semester 2 Examinations 2008/

Module Title: Water Engineering

Module Code: CIVL

School: Building and Civil Engineering

Programme Title: Bachelor of Engineering in Civil Engineering – Year 2

Programme Code: CCIVL_7_Y

External Examiner(s): Mr. J. Kindregan, Mr. J. Lapthorne Internal Examiner(s): Mr TL O’Driscoll, Mr P Kennedy

Instructions: Answer four questions

Duration: 2 hours

Sitting: Summer 2009

Requirements for this examination:

Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.

Q1(a) Describe the preliminary treatment stage of a municipal wastewater treatment plant. Include a number of possible treatment systems that may be used, and reasons for their inclusion. Use sketches to support your answer. (8 marks)

Q1(b) A wastewater treatment plant is required for a town with a population of 55,000PE. Primary treatment is included, and removes 25% of the BOD. Assume a hydraulic load of 220 L/PE/day and BOD concentration of 250mg O 2 /l.

(i) Calculate the total plan area required for the primary settlement tanks. Assume an upward flow velocity of 1.5 m^3 /m^2 /hr. (4 marks)

(ii) Calculate the plan area required for a conventional activated sludge system (0.56 kg BOD/m^3 /day). Design the activated sludge system with a depth of 4m. (4 marks)

(iii) Calculate the F/M ratio of the activated sludge tank if the MLSS is 3500 mg/l. (4 marks)

(iv) The wastewater treatment plant discharges to a local river. The BOD 5 level in the river, upstream of the discharge point is 1.0 mg/L. The minimum flow rate in the river during summer is 2 m^3 /s. If the wastewater is treated to the EU 25/35 standard, what is the BOD 5 concentration in the river, downstream of the discharge point? (5 marks)

Q2(a) A 25,000 PE town receives it’s water supply from a water treatment plant 25km away. A water tower, with a top water level of 55 mOD, has been built within the town to service the local needs. The water level in the supply reservoir in the treatment plant is +11mOD, from where it is pumped to the water tower. The 400 mm diameter rising main has a friction factor of 0.005. The pump shall be designed to discharge 3 times the average water demand. Calculate the following: (i) Maximum pump discharge required (Litres/sec) (3 marks) (ii) Head loss due to friction at the outlet at the town (m) (6 marks) (iii) Total pressure head required (in bar) at the pump. (6 marks)

Q2(b) Calculate the magnitude and direction of the force on a 90 degree bend in a 450mm diameter pipeline, where the flow through the pipeline is 300 litres per second, and pipeline pressure is 6 bar. (10 marks)

Q3(a) Calculate the peak runoff from a car park, with dimensions 150m x 260m. Assume 80% runoff from the paved area, to the drainage system, and a maximum rainfall intensity of 50mm/hr. Cr = 1.3. Use the Modified Rational Equation (below) to calculate the flow rate. Rational Equation Q(l/s) = 2.78.Cv.Cr. A(ha) I(mm/hr) (5 marks) Design a suitable storm drain, using the attached uPVC design chart (Figure A). Use the chart to recommend a required pipe diameter and gradient. (4 marks)

Q3(b) Explain how the Water Framework Directive will improve water quality in Ireland. (5 marks) Describe current problems associated with river water quality in Ireland. (5 marks) Q3(c) Explain how septic tank systems are used to treat wastewater from single domestic dwellings in Ireland. Discuss advantages and disadvantages of this system. Use sketches to support your answer. (6 marks)

Q4(a) Sketch a line diagram of a typical water treatment process. Identify and describe physical and physio-chemical processes used in the water treatment process. (9 marks)

Q4(b) A horizontal flow settlement tank is used in a water treatment plant for particle settlement. The water enters the tank over a weir and flows across the tank with a uniform horizontal velocity of 0.015m/s. The particles have a diameter of 0.1mm and a density of 2650 kg/m^3. Assume a water viscosity ( v) of 1.01 x 10-6^ m^2 /sec. The length of the tank is 8m. Determine the maximum tank depth to ensure that the particle drops to the bottom of the tank.

18 v

v gd^2 (SG^1 )

s

= −

(6 marks)

Q4(c) Discuss the occurrence of Cryptosporidium in water supplies in Ireland. What water treatment methods could be used to prevent these pathogens getting into municipal water supplies? (10 marks)

Q5(a) The following table shows the monthly river inflow to a storage reservoir over a one year period. The demand on the system is 20 x 10 5 m^3 /month.

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec River Inflow (x10 5 m^3 /month)

(i) Calculate the minimum volume of water that must be stored in the reservoir, prior to month 1, to ensure an adequate water supply at all times during the year. (5 marks)

(ii) Calculate the minimum storage capacity of the reservoir. (5 marks)

Q5(b) Determine the maximum moment (in KNm/meter length of wall) at the base of an open 9m deep reinforced concrete tank, which is filled to the top with water. (5 marks)

Q5(c) Describe the different types of pipe materials in common use for the gravity collection of storm-water and foul effluent. List the advantages and disadvantages of each pipe material. (5 marks)

Describe at least two common joints used for connection of these pipes. Use sketches to support your answer. List the advantages and disadvantages of each system. (5 marks)

Figure A